Post passivation interconnect and fabrication method therefor

ABSTRACT

A method of manufacturing a semiconductor structure. The method includes depositing a conductive material over a substrate, and removing a portion of the conductive material to form a conductive structure having a barrel shape. A width of a body portion of the conductive structure is greater than a width of an upper portion and a width of a bottom portion of the conductive structure.

PRIORITY CLAIM

The instant application is a non-provisional application claimingpriority to Provisional Application No. 62/427,786, filed Nov. 29, 2016,the entire content of which is incorporated by reference herein.

BACKGROUND

A semiconductor integrated circuit (IC) includes both active devices,such as transistors and diodes, and passive devices, such as resistersand capacitors. Devices are initially isolated from each other in afront-end-of-line (FEOL) process, and later coupled to each other in aback-end-of-line (BEOL) process in order to perform functionaloperations. The BEOL process includes fabrication of interconnectstructures, such as conductive pads and bumps. Post passivationinterconnects (PPI) are used to connect the conductive pads with thebumps. Electrical connections are made through the conductive pads toconnect the die to a substrate or another die.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross-sectional view of a semiconductor device having a PPIin accordance with one or more embodiments.

FIG. 2 is a flow chart of a method of fabricating a PPI in accordancewith one or more embodiments.

FIGS. 3A-3D are cross-sectional views at various stages of fabrication asemiconductor device in accordance with one or more embodiments.

FIGS. 4A-4B are cross-sectional views at various stages of fabrication asemiconductor device in accordance with one or more embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components, values, operations, materials,arrangements, or the like, are described below to simplify the presentdisclosure. These are, of course, merely examples and are not intendedto be limiting. Other components, values, operations, materials,arrangements, or the like, are contemplated. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures.

As semiconductor technology evolves, a geometrical size of interconnectstructures decreases to increase IC density, lower manufacturing costand improve device performance. The interconnect structures includelateral interconnections, such as metal lines (wirings), and verticalinterconnections, such as contacts and via plugs. The metal lines andvia plugs are formed in inter-metal dialectic (IMD) layers. On top ofIMD layers, conductive pads are formed and connected to bumps throughthe PPI, also referred to as a redistribution line (RDL). In someembodiments, the bumps include solder bumps, copper pillars, or othersuitable bumps. One type of semiconductor packaging is a wafer levelchip scale packaging (WLCSP), in which a die is packaged in a way thatuses the PPI structures to fan out electrical connections for conductivepads to rewire and reposition external terminals at desired locations.

A first insulating layer is formed to isolate the topmost metal line inthe IMD layer from the PPI and a second insulating layer is formed toprotect the PPI from moisture and ions, such as sodium ions, enteringand diffusing into the PPI from the external environment. With smallerprocess geometries, a control of a step coverage and a conformity of thesecond insulating layer is more difficult, thereby increasing a risk ofa crack generating at an interface of a sidewall portion and a bottomportion of the second insulating layer. Additionally, the smallergeometry makes the PPI more susceptible to collapsing during subsequentprocesses. Therefore, the production yield is sensitive to the stepcoverage and the conformity of the second insulating layer.

In some embodiments, a profile of the PPI has a barrel shape. That is, abody portion of the PPI is wider than both an upper portion and a bottomportion of the PPI. In some embodiment, the barrel shape is formed bymultiple etch processes. For example, an anisotropic etch process isfollowed by an isotropic etch process. An undercut at the bottom portionof the PPI of the barrel shape improves step coverage and conformity ofthe second insulating layer as well as the quality and reliability ofthe device. In some embodiments, a profile of the PPI has a trapezoidalshape. The step coverage and conformity of the second insulating layeris improved in comparison with other PPI structures because a sidewallof the bottom portion of the PPI has an obtuse angle with respect to thetop surface of the passivation layer.

FIG. 1 is a cross-sectional view of a semiconductor device 100 inaccordance with one or more embodiments. Semiconductor device 100includes a substrate 110, interconnect structures 112, IMD layers 114, afirst insulating layer 120, at least one PPI 130, a second insulatinglayer 170, and a polymer layer 190. In some embodiments, substrate 110includes silicon, III-V compounds or other bulk semiconductor material.In some embodiments, substrate 110 is a silicon on insulator layer (SOI)substrate or a silicon on sapphire (SOS) substrate. Substrate 110includes an electrical circuitry (not shown). In some embodiments, aplurality of fin structures extends from substrate 110. In someembodiments, contact plugs (not shown), an inter-layer dielectric (ILD)(not shown) and interconnect structures 112 are formed over substrate110. Interconnect structures 112 include metal lines and via plugs,which are formed in IMD layers 114. In some embodiments, the metal linesor the via plugs include at least one of aluminum, copper, copper alloy,tungsten, gold or another suitable conductive material. In someembodiments, IMD layers 114 include a low-k dielectric material, whichhas a dielectric constant lower than 3, or an extreme low-k (ELK)dielectric material, which has a dielectric constant lower than 2.6. Insome embodiments, a combination of metal lines formed in same IMD layer114 is referred to as a metal layer at a same level. The metal lines atdifferent levels are electrically connected through the via plugs toeach other, and through the contact plugs to the electrical circuitry.

A first insulating layer 120 is over IMD layers 114. First insulatinglayer 120 is also referred to as a first passivation layer orpassivation layer 1 (PASS1). In some embodiments, first insulating layer120 includes a single dielectric material, such as silicon dioxide. Insome embodiments, first insulating layer 120 includes compositedielectric materials, such as a combination of undoped silicate glass(USG) and silicon nitride. In some embodiments, a thickness of firstinsulating layer 120 ranges from about 700 nanometers (nm) to about 1200nm. For example, first insulating layer 120 includes a 75 nm siliconnitride and an 850 nm USG. Because first insulating layer is used toprotect interconnect structures 112 and the electrical circuitry fromdamage and contamination, a smaller thickness reduces the protectionfunction, in some instances. However, a greater thickness increasesmanufacturing cost without a significant increase in protection, in someinstances. In some embodiments, first insulating layer 120 includesrecesses 122 exposed in a trench 160. In some embodiments, a depth ofrecesses 122 ranges from 50 nm to about 400 nm. A greater depth reducesthe protection function of first insulating layer 120, in someinstances. In at least one embodiment, PPI via plugs (not shown) areformed in first insulating layer 120 to electrically connect contactpads and a topmost metal line of interconnect structures 112.

Two or more PPIs 130 are over first insulating layer 120. In someembodiments, PPI(s) 130 electrically connect to corresponding contactpads and bumps. In some embodiments, considering a coefficient ofthermal expansion of a die, a greater density of conductive featureshelps prevent warping in a subsequent thermal process. In someembodiments, at least some PPIs 130 are dummy PPIs not connected to acontact pad or a bump. PPI 130 includes at least aluminum, copper,aluminum-copper, gold, tungsten or another suitable conductive material.In some embodiments, PPI 130 includes a same material as interconnectstructures 112. In some embodiments, PPI 130 includes a differentmaterial from interconnect structures 112. For example, PPI 130 includesaluminum and interconnect structures 112 include copper. Adding copperinto PPI 130 and/or interconnect structures 112 helps reduceelectromigration (EM) caused by electrons, in some instances. In someembodiments, an anti-reflective layer, such as titanium nitride ortantalum silicon nitride, is over PPI 130. In some embodiments, thebumps are arranged in a ball grid array (BGA). In some embodiments, thecontact pad includes at least aluminum, copper, aluminum-copper oranother suitable conductive material. An under-bump metallurgy (UBM)structure is between PPI 130 and the bump. In some embodiments, the UBMstructure extends beyond an edge of the bump along a direction parallelto a top surface of PPI 130. In some embodiments, the UBM structuredirectly connects to PPI 130.

In some embodiments, a profile of PPI 130 has a barrel shape. That is, awidth w11 of an upper portion 131 and a width w13 of a bottom portion133 are both smaller than a width w12 of a body portion of PPI 130. Anundercut is formed at a corner between bottom portion 133 and a topsurface of first insulating layer 120. In some embodiments, width w11ranges from about 0.75 micrometers (μm) to about 2 μm, width w12 rangesfrom about 1 μm to about 3 μm and width w13 ranges from 0.75 μm to about2.5 μm. A greater width increases a chip size, in some instances. Asmaller width increases a resistance of PPI 130, resulting in anincrease in a resistive-capacitive (RC) time delay, in some instances.In some embodiments, PPI 130 has a height h11 ranging from about 1.5 μmto about 4.5 μm. A greater height h11 increases a difficulty of asubsequent gap-filling process and/or increases manufacturing costwithout a significant improvement in enhancing an operating speed, insome instances. A smaller height h11 increases the resistance of PPI130, in some instances. Each PPI 130 is separated from adjacent PPI(s)130 by a minimum spacing s11 which is at bottom portion 133. In someembodiments, minimum spacing s11 is equal to or greater than 1 μm. Asmaller spacing s11 also increases the difficulty of subsequentgap-filling process, in some instances. In some embodiments, a minimumspacing between body portions of adjacent PPIs 130 is around 0.9 μm. Asmaller spacing between body portions also increases the difficulty ofsubsequent gap-filling process, in some instances. In such a way, anaspect ratio of PPI 130, which is based on height h11 and spacing s11,is at least 1.5, in some instances. In some embodiments, upper portion131 has an upper angle θ11 ranging from about 100 degrees to about 110degrees, and bottom portion 133 has a lower angle θ13 ranging from about95 degrees to 105 degrees. Upper angle θ11 is between a sidewall and atop surface of PPI 130 and lower angle θ13 is between the sidewall and abottom surface of PPI 130. A smaller or a greater angle increases adifficulty of controlling a conformity of a second insulating layer 170,especially a second dielectric layer 174, in subsequent process(es), insome instances. For example, a smaller upper angle θ11 increases a riskof an overhang around upper portion 131. In some embodiments, a profileof PPI 130 has a trapezoidal shape with tapered sidewalls. Variousprofiles of PPI 130 are discussed below in more detail in associationwith cross-sectional views corresponding to the operations of the flowdiagram.

Second insulating layer 170 is over PPI 130 and first insulating layer120. In some embodiments, second insulating layer 170 is referred to asa second passivation layer or passivation layer 2 (PASS2). Secondinsulating layer 170 includes a first dielectric layer 172 and seconddielectric layer 174. In some embodiments, first dielectric layer 172includes silicon oxide, silicon oxynitride, tetraethoxysilane (TEOS)oxide or another suitable material. In some embodiments, firstdielectric layer 172 includes composite materials. For example, asilicon rich oxide liner and a silicon dioxide layer. In someembodiments, second dielectric layer 174 includes silicon nitride,silicon oxynitride or another suitable material. In some embodiments,first dielectric layer 172 includes a same material as second dielectriclayer 174. In some embodiments, first dielectric layer 172 includes adifferent material from second dielectric layer 174. For example, firstdielectric layer 172 is USG and second dielectric layer 174 is siliconnitride.

In some embodiments where first dielectric layer 172 is silicon oxide orsilicon oxynitride, a thickness of first dielectric layer 172 rangesfrom about 0.6 μm to about 1.8 μm. In at least some embodiments, firstdielectric layer 172 is used to protect PPI 130 and recover damages andcharging effect. Therefore, a smaller thickness of first dielectriclayer 172 reduces the protection function, in some instances. However, agreater thickness of first dielectric layer 172 increases manufacturingcost without providing a significant improvement in recovering fromdamage or charging effect, in some instances. Also, a greater thicknessof first dielectric layer 172 increases a difficulty of subsequentgap-filling process, especially at minimum pitch in a design rule, insome instances. In a thin film process, a conformity is a ratiodetermined by a smallest sidewall thickness t13 to a greatest thicknesst12. In some embodiments, the conformity of the first dielectric layer172 is equal to or greater than 75%. In addition, a sidewall stepcoverage is a ratio determined by an average sidewall thickness and athickness t14 over PPI 130. In some embodiments, the sidewall stepcoverage of first dielectric layer 172 is equal to or greater than 75%.A bottom step coverage is a ratio determined by thickness t14 to athickness t11 over first insulating layer 120. In some embodiments, thebottom step coverage of first dielectric layer 172 is equal to orgreater than 75%. A smaller bottom step coverage of first dielectriclayer 172 negatively affects a step coverage of second dielectric layer174, in some instances.

In some embodiments where second dielectric layer 174 is siliconnitride, a thickness of second dielectric layer 174 ranges from about0.35 μm to about 1.05 μm. In some embodiments, second dielectric layer174 is used to prevent moisture and mobile ions from entering PPI 130.Therefore, a smaller thickness of second dielectric layer 174 increasescontamination of moisture and/or mobile ions, in some instances.However, a greater thickness also increases a difficulty of subsequentgap-filling process, in some instances. In some embodiment, a conformityof second dielectric layer 174 ranges from about 75% to about 85%, asidewall step coverage ranges from about 75% to about 85%, and a bottomstep coverage ranges from about 60% to about 80%. Due to an improveconformity and step coverage, an interface between a sidewall of seconddielectric layer 174 and a bottom portion close to first insulatinglayer 120 has a reduced risk of cracking. A dashed line in FIG. 1indicates a likely location for a crack 180 in other semiconductordevices.

Polymer layer 190 is over second insulating layer 170 and in trench 160.In some embodiments, polymer layer 190 includes epoxy, polymide,benzocyclobutene (BCB), polybenzoxazole (PBO), or another suitablematerial. In some embodiments, polymer layer 190 is photo-sensitive ornon-photo-sensitive. In some embodiments, a thickness of polymer layer190 ranges from about 4.5 μm to about 15 μm. Because polymer layer 190is used to protect the electrical circuitry, interconnect structures,and/or PPI 130 from moisture, mechanical and radiation damage, a smallerthickness reduces a protection of the electrical circuitry and PPI 130,in some instances. However, a greater thickness reduces a thermalconductivity of polymer layer 190, which increases a risk of damage tosemiconductor device 100 due to overheating, in some instances.

FIG. 2 is a flowchart of a method 200 of fabricating a semiconductordevice in accordance with one or more embodiments. One of ordinary skillin the art would understand that additional operations are able to beperformed before, during, and/or after method 200 depicted in FIG. 2, insome embodiments. Additional details of the fabricating process areprovided below with respect to FIGS. 3A-3D and 4A-4B, in accordance withsome embodiments.

Method 200 includes operation 210 in which a first insulating layer isdeposited over a substrate, e.g., first insulating layer 120 oversubstrate 100 in FIG. 1. In some embodiments, the first insulating layerincludes one or more layers, such as oxide, tetraethoxysilane (TEOS),USG, fluorinated silicon glass (FSG), phosphosilicate glass (PSG),boron-doped silicate glass (BSG), boron-phosphor-doped silicate glass(BPSG), silicon nitride, silicon carbide or silicon oxynitride. Theformation of the first insulating layer includes a deposition process,such as chemical vapor deposition (CVD), physical vapor deposition(PVD), atomic layer deposition (ALD), thermal oxidation or anothersuitable process. In some embodiments wherein the first insulating layerincludes more than one material, the formation of each material includesa same or different deposition processes.

Method 200 continues with operation 220 in which a conductive materialis deposited over the first insulating layer, e.g., first insulatinglayer 120 in FIG. 1. In some embodiments, the conductive materialincludes aluminum, aluminum alloys, copper, copper alloys,aluminum-copper, titanium, nickel or another suitable material. Theformation of the conductive material includes a deposition process, suchas CVD. In some embodiments, the formation of the conductive materialincludes sputtering, evaporation, electrolytic plating, electro-chemicalplating (ECP), electroless plating or printing. In some embodiments, theconductive material includes multiple components by using an adhesionmaterial, such as titanium, chromium or titanium tungsten. One ofordinary skill in the art would understand that, in order toelectrically connect a topmost metal line in the IMD layers, e.g., IMDlayers 114 in FIG. 1, and a contact pad (I/O pad), at least one PPI viaplug is formed in an opening in the first insulating layer. The openingin the first insulating layer is made by removing a portion of the firstinsulating layer using a photoresist defined etch process to expose atleast a portion of a topmost metal line or contact pad. The formation ofthe at least one PPI via plug includes a photolithography process, anetch process and a deposition process.

Method 200 continues with an optional operation 230 in which a firstetch process is performed onto the conductive material. The first etchprocess helps to define a PPI from the conductive material. A mask layersuch as a photoresist is patterned to determine a pattern of the PPI andto protect the PPI during the etch process. A trench is formed betweenthe adjacent PPIs during the first etch process, e.g., trench 160between adjacent PPIs 130 in FIG. 1. In some embodiments, an upperportion of the PPI is formed to have an upper angle between a sidewalland a top surface of the PPI and extending away from a center of thePPI. In some embodiments, the upper angle ranges from about 100 degreesto about 110 degrees. In some embodiments, the upper portion has arounded corner. In some embodiments, a body portion of the PPI is alsoformed during the first etch process. In some embodiments, the firstetch process is an anisotropic etch process. In some embodiments, theanisotropic etch process is a dry etching or a plasma-assisted etching,such as reactive ion etch (RIE), high density plasma (HDP) etching,transformer coupled plasma (TCP), inductively coupled plasma (ICP),cyclotron resonance (ECR), capacitively coupled plasma (CCP) or sputteretching. In some embodiments, the anisotropic etch process is a wetetching.

The plasma-assisted etching includes a chemical reaction by radicals andions and a physical bombardment onto a process surface. The chemicalreaction occurs between an etchant and the process surface, with orwithout plasma, while a volatile product is pumped away. In someembodiments where the first etch process is RIE, an injected gas,includes CCl₄, BCl₃, B₂Cl₆, BBr3, Cl₂, HCl, HBr, CF₄, or the like, anetchant flow from about 20 sccm to 200 sccm and at a pressure rangesfrom about 50 mTorr to about 300 mTorr. The etchant gas is ionizedthrough a dissociative process by plasma. In some embodiments, theplasma is generated from a first electrode plate with a radio frequency(RF) source power ranging from about 50 to about 2000 watts and the biaspower of a second electrode plate is in a range from about 50 watts toabout 1000 watts. An etching behavior is affected by various processparameters such as RF power and bias power. For example, when a ratio ofRF power/bias power is lower, the physical bombardment increases,resulting in a more anisotropic etching behavior. In contrast, a higherratio of RF power/bias power results in a more isotropic etchingbehavior.

In some embodiments, the etching behavior is determined by aplasma/radical ratio. The injected gas rarely reacts with the processsurface that has been etched while free radicals are the major reactantspecies. Therefore, a relatively higher plasma/radical ratio generatesmore ions so that an efficiency of the physical ion bombardment isgreater than the chemical reaction by the radicals.

Next, following operation 230, method 200 continues with operation 232in which a second etch process is performed to form a conductivestructure, e.g., PPI 130 in FIG. 1. The PPI is formed to have a barrelshape during the second etch process. In some embodiments, a bodyportion of the PPI is formed during the second etch process. In someembodiments, the bottom portion of the PPI has a lower angle, which isbetween the top surface of the first insulating layer and a sidewall ofthe bottom portion, toward the center of the PPI in a range from about95 degrees to 105 degrees. In some embodiments, the second etch processis an isotropic etch process. In some embodiments, the second etchprocess is a wet etching. In some embodiments, the second etch processis a plasma-assisted etching. In some embodiments, the first etchprocess uses a same technique as the second etch process. In someembodiments, the first etch process uses a different technique from thesecond etch process. For example, the first etch process is an argonsputtering and the second etch process is a plasma-assisted etching.Other inert gas or other gas mixtures which would not react with the PPImay be used, in some instances. As another example, the first etchprocess uses a plasma-assisted etching and the second etch process usesa wet etching.

In some embodiments where the second etch process is a plasma-assistedetching, such as RIE, a ratio of RF power/bias power of the second etchprocess is smaller than a ratio of RF power/bias power of the first etchprocess. In such a way, the first etch process has a relatively greaterphysical ion bombardment than chemical radical reaction, and the secondetch process has a relatively greater chemical radical reaction thanphysical ion bombardment, thereby resulting in a more anisotropicetching behavior than an isotropic etching behavior during the firstetch process, and a more isotropic etching behavior than an anisotropicetching behavior during the second etch process. In some embodiments, aratio of plasma/radical of the first etch process is higher than a ratioof plasma/radical of the second etch process. As a result, the firstetch process is similar to anisotropic etching because of a relativelygreater physical ion bombardment, and the second etch process is similarto isotropic etching because of a relatively greater chemical reaction.

In some embodiments, because a greater pressure increases a mean freepath of ions in the plasma, which decreases the physical ion bombardmentenergy transferred to the process surface, the first etch process isperformed at a relatively lower pressure than the second etch process.

In at least one embodiment where the PPI includes aluminum and the firstetch process is a wet etching, an etching solution includes hot (fromabout 40 degrees Celsius to about 50 degrees Celsius) H₃PO₄, CH₃COOH,HNO₃ and H₂O.

In some embodiments, after the first etch process, a polymer material isformed along sidewalls and a bottom surface of the trench and a topsurface of the PPI. In some embodiments, the polymer material is blanketdeposited to cover sidewalls of the trench. In some embodiments, thepolymer material is formed by a plasma process using a carbon-richhydrofluorocarbon plasma, such as difluoromethane. In some embodiments,a thickness of the polymer material ranges from about 10 nm to about 50nm. Afterward, a portion of polymer material is removed from the topsurface of the PPI and from the bottom surface of the trench. Thepolymer remains along the sidewalls of the trench. Next, the second etchprocess is performed to cause a barrel shape. The sidewall polymer isthen stripped using an oxygen plasma, in some embodiments.

In at least one embodiment, a top portion of the first insulating layeris removed during the second etch process and a recess is formed to havea depth in range from about 50 nm to about 200 nm.

Alternatively, following operation 220, method 200 continues withoperation 240 in which a third etch process, e.g., etch process 454 inFIG. 4A, is performed to form a conductive structure. The conductivestructure, also referred to as the PPI, has a trapezoidal shape withtapered sidewalls. A width of an upper portion is smaller than a widthof a bottom portion of PPI. In some embodiments, the third etch processis an anisotropic etch process. In some embodiments, the third etchprocess is a combination of an anisotropic etch process and an isotropicetch process. In some embodiments, the upper portion of the PPI has anupper angle ranging from about 95 degrees to about 105 degrees. Theupper angle is between a top surface and a sidewall of the PPI. Asmaller upper angle increases a difficulty of controlling the conformityof the second dielectric layer in a subsequent process, in someinstances. A greater upper angle increases a risk of generating voids inthe trench, in some instances.

Following operation 232 or operation 240, method 200 continues withoperation 250 in which a second insulating layer is deposited over theconductive structure, e.g., second insulating layer 170 in FIG. 1. Thesecond insulating layer partially fills the trench between theconductive structures. In some embodiments, the second insulating layerincludes a first dielectric layer, e.g., first dielectric layer 172 inFIG. 1, and a second dielectric layer, e.g., second dielectric layer 174in FIG. 1. In some embodiments, the first dielectric layer includessilicon oxide, TEOS, USG, PSG, silicon oxynitride, silicon nitride oranother suitable material. In some embodiments, the first dielectriclayer uses a same material as the first insulating layer. In someembodiments, the second dielectric layer includes silicon nitride,silicon oxynitride, silicon carbide or another suitable material. Insome embodiments, the second dielectric layer uses a same material asthe first dielectric layer. In some embodiments, the second dielectriclayer is different from the first dielectric layer. The formation of thesecond insulating layer includes a deposition process, such as CVD, PVD,ALD, thermal oxidation or another suitable process. In some embodimentswhere the deposition process is CVD, the second insulating layer isformed by using a plasma-enhanced CVD (PECVD), high-density plasma CVD(HDPCVD) or low-pressure CVD (LPCVD). In some embodiments, the formationof the first dielectric layer uses a same technique as the seconddielectric layer. In some embodiments, the formation of the firstdielectric layer uses a different technique from the second dielectriclayer. In some embodiments, the second insulating layer is patterned tocover a peripheral portion of the contact pad and to expose a centerportion of the contract pad. In some embodiments, the second insulatinglayer includes more than two dielectric materials.

Method 200 continues with operation 260 in which a protective layer isdeposited over the second insulating layer, e.g., polymer layer 190 oversecond insulating layer 170 in FIG. 1. The protective layer is formedover the second insulating layer and fills the trench between the PPIs.The formation of the protective layer includes a deposition process,electromagnetic compatibility (EMC) coating, spin coating or anothersuitable process. In some embodiments, the protective layer includesepoxy, polyimide, BCB, PBO or another suitable material. In someembodiments, the protective layer includes a soft, organic material.

In some embodiments, additional operations are included in method 200,such as forming the conductive structure by using a fourth etch processbefore or after the second etch process. In some embodiments, multipleoperations for method 200 are performed simultaneously. For example, insome embodiments operation 230 and operation 232 are performedsimultaneously.

FIGS. 3A-3D are cross-sectional views of a semiconductor device 300during various stages of processing in accordance with some embodiments.FIG. 3A is a cross-sectional view of semiconductor device 300 followingoperation 220. Semiconductor device 300 includes elements similar tosemiconductor device 100 and a last two digits of like elements are thesame. Semiconductor device 300 includes a substrate 310, interconnectstructures 312, IMD layers 314, a first insulating layer 320 and aconductive material 330′. In some embodiments, a diffusion barrier layeris formed between first insulating layer 320 and conductive material330′.

FIG. 3B is a cross-sectional view of semiconductor device 300 followingoperation 230. A mask layer 340 such as a photoresist is formed overconductive material 330′ to pattern PPIs 330 and/or the conductive pad.During a first etch process 350, an opening of trench 360 is formedbetween PPIs 330 and an upper portion 331 of PPI 330 is formed to have aheight h31′. In some embodiments, a body portion 332 of PPI 330 ispartially or fully formed during first etch process 350.

FIG. 3C is a cross-sectional view of semiconductor device 300 followingoperation 232. A bottom portion 333 of PPI 330 is formed during a secondetch process 352. In some embodiments, PPI 330 has a height h31 rangingfrom about 1.2 to about 2 times than height h31′. A greater height h31increases a difficulty of a subsequent gap-filling process, in someinstances. A smaller height h31 increases a quantity of defects aroundbottom portion 333, resulting in a low production yield, in someinstances. A recess 322 is formed in first insulating layer 320 duringsecond etch process. In some embodiments, when mask layer 340 is thephotoresist an oxygen plasma ashing process is performed to expose thetop surface of PPI 330 following second etch process 352. In at leastone embodiment, where second etch process 352 is a plasma-assistedetching, mask layer 340 is removed and bottom portion 33 is formedsimultaneously during second etch process 352.

FIG. 3D is a cross-sectional view of semiconductor device 300 followingoperation 250. A second insulating layer 370 is formed over PPI 330 andfirst insulating layer 320. In some embodiments, second insulating layer370 includes a first dielectric layer 372 and a second dielectric layer374. In some embodiments, a bottom surface of PPI 130 and a bottomsurface of first dielectric layer 372 is between a top surface and abottom surface of first dielectric layer 372. Because a width of bottomportion 333 is reduced in comparison with a body portion of PPI 330, aspacing at a bottom portion of trench 360 is relatively wider during aformation of second dielectric layer 374, resulting in an improvedconformity of second dielectric layer 374. Further, due to the improvedconformity of second dielectric layer 374, a step coverage at aninterface between a bottom portion and sidewall of second dielectriclayer 374 is improved and a risk of cracks in second dielectric layer372 is reduced with respect to other approaches.

FIGS. 4A-4B are cross-sectional views of a semiconductor device 400during various stages of processing in accordance with some embodiments.FIG. 4A is a cross-sectional view of semiconductor device 400 followingoperation 240. Semiconductor device 400 includes elements similar tosemiconductor device 100 and a last two digits of like elements are thesame. Semiconductor device 400 includes a substrate 410, interconnectstructures 412, IMD layers 414, a first insulating layer 420, recesses422, PPIs 430, second insulating layer 470 and polymer layer 490. PPI430 includes an upper portion 432 and a bottom portion 434. Secondinsulating layer 470 includes a first dielectric layer 472 and a seconddielectric layer 474.

In some embodiments, PPI 430 is formed by an etch process 454. Etchprocess 454 includes a dry etching and/or a wet etching. In someembodiments, a profile of PPI 430 has a trapezoidal shape. A width w43is greater than a width w41. Because an upper angle θ41 and a lowerangle θ43 are supplementary angles, upper angle θ41 and lower angle θ43add up to 180 degrees. Therefore, lower angle θ43 is in a range fromabout 75 degrees to about 85 degrees. In some embodiments, each PPI 430is separated from adjacent PPI(s) by a minimum spacing s41 at bottomportion 434. In some embodiments, minimum spacing s41 is equal to orgreater than 1 μm. A bottom step coverage is a ratio determined bythickness t44 to a thickness t41 over first insulating layer 420. Insome embodiments, the bottom step coverage of first dielectric layer 472is equal to or greater than 75%.

By adjusting the profile of the PPI, a conformity and sidewall stepcoverage of the second dielectric layer is improved with respect toother approaches, thereby reducing a risk of generating a crack near abottom portion of a PPI. In at least one approach, the profile isdetermined by the etching behavior when manufacturing the interconnectstructure. Moreover, the improved sidewall conformity and sidewall stepcoverage provides more choices of equipment/apparatus, resulting in areduced manufacturing cost and increased production yield.

One aspect of this description relates to a method of manufacturing asemiconductor structure. The method includes depositing a conductivematerial over a substrate, and removing a portion of the conductivematerial to form a conductive structure having a barrel shape, wherein awidth of a body portion of the conductive structure is greater than awidth of an upper portion and a width of a bottom portion of theconductive structure.

Another aspect of this description relates to a method of manufacturinga PPI. The method includes depositing a first passivation layer over asubstrate, depositing a conductive material over the first passivationlayer, etching the conductive material to form at least two conductivelines, wherein the etching operation has two etching steps and apressure of a first etching step is lower than a pressure of a secondetching step, depositing a second passivation layer over the at leasttwo conductive lines, and depositing a polymer layer over the secondpassivation layer

Still another aspect of this description relates to an IC device. The ICdevice includes a first passivation layer over a substrate, aredistribution line over the first passivation layer, a secondpassivation layer over the redistribution line, and a polymer layer overthe second passivation layer, wherein the redistribution line has abarrel-shaped profile.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of manufacturing a semiconductorstructure, comprising: depositing a conductive material over asubstrate; and removing a portion of the conductive material to form aconductive structure having a barrel shape, wherein a width of a bodyportion of the conductive structure is greater than a width of an upperportion and a width of a bottom portion of the conductive structure, andan entirety of a sidewall of the conductive structure has a curvedconvex surface.
 2. The method of claim 1, wherein removing the portionof the conductive material comprises: performing an anisotropic etchingprocess to form an upper portion of the conductive structure, whereinthe upper portion of the conductive structure has a trapezoidal shape;and performing an isotropic etching process to form a bottom portion ofthe conductive structure, wherein the bottom portion of the conductivestructure has an undercut.
 3. The method of claim 2, wherein performingthe isotropic etching process comprises performing a wet etching.
 4. Themethod of claim 1, wherein removing the portion of the conductivematerial comprises: performing a first reactive ion etching (RIE)process to form an upper portion of the conductive structure; andperforming a second RIE process to form a bottom portion of theconductive structure, wherein a radical/plasma ratio of the first RIEprocess is greater than a radical/plasma ratio of the second RIEprocess.
 5. The method of claim 1, wherein removing the portion of theconductive material comprises: performing a first plasma etching processto form an upper portion of the conductive structure; and performing asecond plasma etching process to form a bottom portion of the conductivestructure, wherein a RF power/bias power ratio of the second plasmaetching process is greater than the first plasma etching process.
 6. Themethod of claim 1, further comprising: forming a polymer material alongsidewalls of the unremoved portion of the conductive material.
 7. Themethod of claim 1, further comprising: depositing a first insulatinglayer over the substrate; and depositing a second insulating layer overthe conductive structure, wherein a recess is formed in the firstinsulating layer during the removing operation.
 8. The method of claim7, wherein depositing the second insulating layer comprises: forming therecess to have a depth in a range from about 50 nanometers (nm) to about200 nm.
 9. The method of claim 7, wherein depositing the secondinsulating layer comprises: depositing a first dielectric layer along atop surface and sidewalls of the conductive structure, and a top surfaceof the recess; and depositing a second dielectric layer along the firstdielectric layer, wherein a sidewall step coverage of the seconddielectric layer ranges from about 75% to about 85%.
 10. The method ofclaim 7, wherein depositing the second insulating layer comprises:depositing a first dielectric layer along a top surface and sidewalls ofthe conductive structure, and a top surface of the recess; anddepositing a second dielectric layer along the first dielectric layer,wherein a conformity of the second dielectric layer ranges from about75% to about 85%.
 11. A method of manufacturing a post passivationinterconnect (PPI), comprising: depositing a first passivation layerover a substrate; depositing a conductive material over the firstpassivation layer; etching the conductive material to form at least twoconductive lines, wherein the etching operation has two etching stepsand a pressure of a first etching step is lower than a pressure of asecond etching step; depositing a second passivation layer over the atleast two conductive lines; and depositing a polymer layer over thesecond passivation layer.
 12. The method of claim 11, wherein patterningthe conductive material comprises: removing a portion of the conductivematerial to form the at least two conductive lines to have a barrelshape, wherein a width of a body portion of the at least two conductivelines is greater than a width of an upper portion of the at least twoconductive lines and a width of a lower portion of the at least twoconductive lines.
 13. The method of claim 12, wherein removing theportion of the conductive material comprises: forming an upper portionof the at least two conductive lines to have an upper angle ranging fromabout 100 degrees to about 110 degrees, and a lower portion of the atleast two conductive lines to have a lower angle ranging from about 95degrees to 105 degrees, wherein the upper angle is between a top surfaceand a sidewall of each of the at least two conductive lines and thelower angle is between the sidewall and a bottom surface of each of theat least two conductive lines.
 14. The method of claim 11, whereinetching the conductive material comprises: removing a portion of theconductive material to form the at least two conductive lines to form atrapezoidal shape.
 15. The method of claim 11, wherein etching theconductive material to form the at least two conductive lines comprises:forming the at least two conductive lines to have a height from about0.75 times to about 3 times than a spacing between the at least twoconductive lines.
 16. The method of claim 11, wherein depositing thesecond passivation layer comprises: depositing a first dielectricmaterial over the at least two conductive lines; and depositing a seconddielectric material over the first dielectric material, wherein a bottomstep coverage of the second dielectric material ranges from about 60% toabout 80%.
 17. The method of claim 16, wherein depositing the seconddielectric material comprises: depositing a silicon nitride to have athickness in a range from about 0.35 micrometers (μm) to about 1.05 μm.18. A method of manufacturing a semiconductor structure, comprising:depositing a conductive material over a substrate; anisotropicallyetching the conductive material to define a conductive material patternin the conductive material, wherein the conductive material pattern hasa first height from a top surface of the conductive material to a bottomsurface of a recess formed by the anisotropic etching; isotropicallyetching the conductive material pattern to define a post passivationinterconnect, wherein the post passivation interconnect has a secondheight from a top surface of the post passivation interconnect to abottom surface of a recess formed by the isotropic etching, and thesecond height is greater than the first height.
 19. The method of claim18, wherein the isotropically etching of the conductive material patterncomprises forming the recess extending into the substrate.
 20. Themethod of claim 18, wherein the isotropically etching of the conductivematerial pattern comprises forming the post passivation interconnecthaving a rounded sidewall.